1. Field of the Invention
This invention relates to semiconductor chip packages, and more specifically to lowpin-count chip packages and manufacturing methods thereof.
2. Description of the Related Art
FIG. 1 is a low-pin-count chip package 100 according to a preferred embodiment disclosed in R. O. C. Publication No. 348306 entitled “Device Having Resin Package And Method Of Producing The Same”. The low-pin-count chip package 100 includes a chip 110 sealed in a package body 120. The active surface of the chip 110 is provided with a plurality of bonding pads 110a electrically connected to a plurality of connection pads 130. The backside surface of the chip 110 is exposed from the package body 120 through a conductive adhesive layer 112. The connection pads 130 are located at the periphery of the chip 110 and exposed from the lower surface of the package body 120 for making external electrical connection. Since the package body 120 does not cover the exposed lower surface of the connection pads 130, it can not firmly lock the connection pads 130.
The connection pads 130 are usually made of metal with good electrical conductivity such as copper but the package body 120 is made of insulating material such as epoxy molding compound. Accordingly, the bond between connection pads 130 and the package body 120 is relatively weak and the difference of the coefficient of thermal expansion (CTE) therebetween is very large. Because of the CTE mismatch, stresses are induced at the interface between the connection pads and the plastic package body as the conventional package experiences temperature cycling. The stresses, in turn, result in the delamination at the metal-plastic interface. When the delaminations had occurred at the plastic-metal interface, moistures from the environment are easy to penetrate into the plastic package body and accumulate in the delaminated area. Once moisture accumulates in the package, rapid temperature ramp-up will cause the moisture to vaporize and expand, thereby inducing an hygrothermal stresses in the delaminated area which causes the surrounding plastic package body to popcorn. One of the most common occurrence of package popcorning occurs when the package described above is surface-mounted to a printed wiring board during the Infra-Red reflowing process.
Further, since the package body 120 only seals one side of the chip 110, moisture and/or ionic contamination from the atmosphere can sometimes penetrate through the bonding lines between the epoxy molding compound and the chip 110, which can cause reliability problems, i.e. a great reduction of the operating life of package. This phenomenon is becoming more and more critical as the semiconductor industry moves towards packaging electronic devices into a smaller and smaller packages.